Transmissions for motor vehicles have already become known in multiple versions. Manual-shift transmissions, in which the driver manages the gear change, have been and continue to be widely used because of the cost advantage of such transmissions. In addition to these manual-shift transmissions operated by the driver, automatic transmissions have already become known that can be fully automatically shifted transmissions having a hydrodynamic converter and a transmission of the planetary type connected downstream thereof. Such known automatic transmissions are regularly equipped with a parking lock by which the output shaft of the transmission and with it the drivetrain can be blocked so that an unintended rollaway of the vehicle can be prevented. The automatic transmission is locked in this context in that the driver of the vehicle sets the selection lever in a position P, which causes the output shaft of the transmission to be blocked via actuation mechanics in the form of, for example, tie rods or connecting rods.
In addition to these known manual transmissions and the described automatic transmissions, using automated-shift transmissions has already become known in motor vehicles in which an actuator in the form of, for example, an electric motor or two electric motors is used for the select operation and shift operation in order to be able to carry out the gear change in a manner controlled by program or also as required by the driver.
The use, the comfort and the operating safety of vehicles, especially passenger vehicles, is decisively affected by the transmission. A prerequisite for fuel-efficient driving is driving at a low speed and an appropriately high torque. The greater the gear ratio spread allowed by the transmission and the simpler the shifting, the more this may be accomplished, which is why automatic and automated-shift transmissions are increasingly being used.
Such an automated-shift transmission with the actuators, the clutch for disengaging the drivetrain and the control devices for the operation of a transmission is designed as a “by-wire” system in which the actuator or actuators are driven via electronic control pulses and a mechanical force transfer path between the selection lever disposed in the vehicle and the transmission is no longer provided. Also, in such an automatically actuated transmission in the form of, for example, an automated-shift transmission or a twin-clutch transmission having two clutches and an actuating mechanism driven by electric motor, it is desirable to provide a parking lock so that the vehicle equipped with it may be prevented from unintentionally rolling away.
Moreover, for the operating safety of the vehicle, it is important that the ignition key may only be removed if the parking vehicle is parked in a secure braked or blocked state, and that this state may not be cancelled in an uncontrolled manner. For driving comfort it is important that the automated or automated-shift transmission spontaneously react to a driver-controlled removal of the securely braked or blocked state and that an immediate start be enabled without in the process causing lags, accelerations or bucking that is sensed by the occupants as a nuisance.